Device for locking a rotatable drawing head

ABSTRACT

A single operating lever control for locking and unlocking a rotatable head on a drafting machine wherein a lock pawl is released from engagement with the teeth of a ratchet disc. A thumb operated lever extends along the side of the conventional hand knob and may be operated in one of two ways. Upon direct inward movement, the pawl is released only so long as the thumb lever is held. In the other mode of operation, the thumb lever is locked so that the lock pawl is retained out of ratchet disc engagement.

United States Patent Wackerfuss DEVICE FOR LOCKING A ROTATABLE DRAWINGHEAD Inventor: Otto Wackerfuss, Wilhelmshaven, Germany Assignee: FranzKuhlmann KG, Prazisionsmechanik und Maschinenbau, Wilhelmshaven, GermanyFiled: Nov. 28, 1969 Appl. No.: 880,686

Foreign Application Priority Data NOV. 29, 1968 Germany ..P 18 ll 805.3

U.S. Cl. ....33/79 R Int. Cl ..B43l 13/08 Field of Search ..33/79 R, 79A, 79 B, 79 C,

all:

June 6, 1972 References Cited UNITED STATES PATENTS 1,877,340 9/1932Kuhlmann ..33/79A FOREIGN PATENTS OR APPLICATIONS 944,298 7/1949 Germany..33/79 R 1,060,287 6/1959 Germany. ..33/79 R 509,935 1/1955 Italy 33/79R Primary ExaminerI-Iarry N. Haroian Attorney-Dennison, Dennison,Townshend & Meserole [57] ABSTRACT A single operating lever control forlocking and unlocking a rotatable head on a drafting machine wherein alock pawl is released from engagement with the teeth of a ratchet disc.A

-thumb operated lever extends along the side of the conven- 8 Claims, 7Drawing Figures PATEHTEUJUH 6 I972 3.667. 126

SHEET 2 or v3 hire/liar GT7- 0 wn mzn ss DEVICE FOR LOCKING A ROTATABLEDRAWING HEAD This invention concems'drawing instruments and moreparticularly a device for locking a rotatable drawing head. In thisdevice shifting members are operated with one single operating thumbmember which is movable toward the middle of a hand knob, and which actsthrough a spring-loaded push rod on a rotatable pawl which engages aratchet disc. This disc in turn is securely attached to a supportingstructure to which are connected the arms of a conventional draftingmachine. The pawl is on the underside of a base having a vemier scalewhich is attached to pivot on the supporting structure, and whichsupports on its top side the knob and the operating member and the pushrod, which is coupled with the pawl by means of a transmission memberwhich engages the pawl through the base.

In one prior art locking device of this general sort, the operatingmember is securely coupled directly with the push rod, so that thepressure of the operating member toward the middle of the knob causes adirect swinging over of the pawl, out of contact with the ratchet disc.In this case, the elastic trip release of the lock adjustment deviceoccurs in a simple operation, however a permanent release of the lockadjustment device is possible only through an additional turn of theoperating member around the drawing head. Such an operation of the handgrip with the thumb placed on the periphery thereof requires movement ofthe thumb along the periphery of the drawing head which requires eithera contortion of the hand in relation to the hand grip or one moresegment in the thumb. The aforementioned movements of the thumbtherefore necessitate a more or less disadvantageous loosening of thehand from the hand grip of the drawing head. Hence, the feeling of asecure hold on the drawing head in the particular position is more orless lost to the operator. Such a manipulation of the locking device isunsatisfactory.

In another prior art device, the movement of the thumb along theperiphery of the drawing head is not necessary. There is even providedfor the permanent release of the locking device a second element whichis directly below the member used for operation of the locking deviceand which secures the first elementin the inwardly depressed position.In this model, one operating member must connect with the other.

The object of this invention is the construction of a locking devicethat is operable with one single operating member without grasping bythe thumb and without additional peripheral manipulation.

This problem is solved by a locking device of the sort illustratedherein, in which the push rod is pivoted to a rotatably positionedintermediate link on the base and the operating member is formed as anangle lever, of which one arm serves as a thumb lever. The other armwhich lies within the knob is rotatably coupled with the intermediatemember and rotates, relative to this, only toward the middle of theknob. The operating member is locked in one position after a horizontalswing and also relative to the intermediate member, in which positionthe pawl comes out of contact with the ratchet plate. With thisconstruction it is also possible, with one single lever attached to theknob, to achieve a temporary and also permanent pawl release of theratchet device, without necessitating a change of .position of the thumbwith relation to the operating member. The thumb lever therebyaccomplishes a purely swiveling movement for the temporary release,while for the permanent tripping a swiveling movement directed towardthe middle of the knob is coupled with an inwardly directeddisplacement. This is possible without change of the thumb positionrelative to the periphery of the knob, whereby the knob remains securelyand stably locked by the left hand, which is advantageous for theaccurate operation of the drawing head.

According to a preferred embodiment of the invention, the arm within theknob is shorter than the thumb lever, is linked at its free end to theintermediate member and has a stop with which it abuts the intermediatemember when activated by a spring. The arm lying within the knob comesinto contact with a head on the intermediate member, whereby thepivoting motion is limited to one direction. The structure of the innerarm being shorter than the thumb lever and consequently the position ofthe link connection being lower than the upper end of the thumb levergives a secure and efficient pivot for the resilient tripping of thelocking device so that less strength is required for operation.

In a further feature of the invention, the inner arm is forked and theintermediate member is a double layer, whereby the push rods are setbetween the levers of the intermediate member and this within the forkedend of the inner arm. This feature provides for the uniform applicationof force and consequently the satisfactory operation of the operatingmember.

According to a further feature of the invention, the intermediate memberis pivoted on a bearing support which is secured onto the base, and theoperating member is hollow and engages the bearing support. Thisembodiment allows a compact structure.

A singular simplification of the structure is given in that a furtherfeature of the invention shows that the bearing support has a catch forthe spring which activates the pawl and a recess for the spring whichbiases the operating member, and which is structured as a coil springand engages a projection on the inner side of the angle lever andsupports an abutment for a stop within the thumb lever. This refinementis especially advantageous with all abutments are united in one singlestructural element. This provides on one hand an economization of spaceand on the other hand simplified production.

Another feature of the invention is that the knob has a detachable capwhich supports a cylindrical, inwardly turned collar with a peripheralridge which catches in a corresponding peripheral groove in the bottomcylindrical portion of the knob. With this construction, it is possible,although the shifting members inside the knob are easily accessible, tomount retaining latches or the like inside, without modification of theflat external shape. Through the use-of a relatively long ring whichrests against the wall in the lower cylindrical portion of the knob, acompletely secure locking of the cap is obtained.

In the drawings:

FIG. 1 is a vertical section through a drawing head;

FIG. 2 is an enlarged section along linesII-II of FIG. 1;

FIG. 3 is a view similar to FIG. 1 of the shifting members in theresilient release position in the knob;

FIG. 4 is an enlarged detail view of portions of FIG. 3;

FIG. 5 is a view similar to FIG. 3, wherein the shifters are in thepermanent release position;

FIG. 6 is an enlarged detail view of portions of FIG. 5; and

FIG. 7 is a plan view of the drawing head with the cap removed.

Reference is now made specifically to the drawings wherein likereference numerals designate similar parts throughout several views.

On rods 1 of a drafting machine is a drawing head 2 with its fixedsupport 3. In the support 3 is a bearing 4 secured thereto by screws. Ascale square 6 is secured within bearing 4 by a rotatable bearingelement 6a. The bearing element 6a is attached securely as by screws toa base 8, which supports a knob 10. The upper part of knob 10 is formedas a detachable cap 11. To the scale square 6 is attached thestraightedge 5 (FIG. 7) and on the other side thereof is attached baseshield 7 in order to protect the drawing head. In order to determine theangular displacement of the angle device of the scale square 6, a vemierplate 9 is securely attached to the support 3 and has thereon an anglegraduation scale. The rotatable base 8 opposite this vemier plate, whichis securely attached to the scale square 6, is provided with a vernierscale.

On the side of support 3 which is toward the base 8 is attached aratchet plate or disc 12, with which a pawl 13 cooperates. The pawl ispivoted on the underside of base 8 by means of a pin 13a, which alsoserves as support for transmisof the structure I sion member '14'engaging through base 8, which, through drivepin 14a, is connected withthe pawl 13. The ratchet plate 12 is so formed that locking of thedrawing head is possible aftera rotation of 15.

For the operation of the pawl 13, the angled end of the transmissionmember 14 engaging through base 8 is connected with a push rod 15, whichengages a short diameter end pin la through abore in the transmissionmember 14 and is secured by means of a spr'ing 15b. The other end of thepush rod 15 is linked with an intermediate member or link 18, which isformed a adouble lever, pivotedby means of a bolt 16. The intermediatemember 18 is rotatably mounted on a bearing block 20 (FIG. 2) on thebase 8 by means ofa bearing bolt 19. Between the-two levers of theintermediate member 18 is a spacer 19a. The operation of these shiftingmembers within the.knob,10 is instituted by an operating member 17.which is formedas an angle lever, whereby one arm 17a extends throughan opening a into the inside of the knob 10 and with its bifurcated endis pivotably connected by the bolt 16 with the intermediate-member 18.The operating member 17 is hollow and engages the bearing block 20. Thearm 17b lying outside the knob serves as a thumb lever. A pin 22 on thebifurcated arm 17a comes into contact with intermediate arm 18in'.response to a coil spring 21 acting on the operating member 17,andthereby limits the pivoting movement of the operating member 17' withrespect to the intermediate member to a radial outward direction withrespect to the knob. I t

The bearingblocklo has a recess20a for housing the coil spring 21- whichengages a projection 25 integral with and within theoperating member 17.On the end of the bearing blocklying within knob 10 is formed a catch 26on which one end of a tension spring 24 is engaged. This spring isconnected with the transmission member 14, and hereby the pawl 13 isurged against the ratchet plate 12. On the opposite end the bearingblock 20 has an'abutment 20b with which stop 23 in the form of atransverse rod cooperates, and which is within operating member 17. 1

The detachable capot' the knobhas an inwardly oriented ring-1 1a, whichhas a ridge at its lower end which fits into-a corresponding groove inthe cylindrical: member 10b of the knob. -R ec.esses 11b and 11c in thering 11a guarantee complete freedomof movement of the shifting memberslying within the knob. 1

The drawing head-described is operated as follows. If the scale square 6is to be swung with its drawing rules 5 out of a certain angularposition determined by an engagement of the pawl 13, the thumb lever 17aof the operating member 17 is moved by lifting-movement of the thumb inthe direction toward the knob shown in FIGS. 3 and 4, 'whereby theintermediate member 18 limits the pivoting movement by contact with astop 27. Hereby the intermediate member 18 pivots, .whereby the pin 22in contact withthe intermediate member causes the simultaneous movementof the intermediate member 18 and the operating'member '17. The movementof the intermediate member 18 causes displacement of the push rodagainst the bias of the spring 24, whereby the transmission member 14and the pawl 13 coupled with it pivot outwardly around the pin 13a, andfree the pawl from the ratchet plate 12. Now the scale square can bepivoted in relation to the'support 3, so long as the thumb lever 17bremains in the upward pivoted position. After release of the thumb lever17b, the pawl 13, in response to spring 24, relocks in the next ad- 7jacent groove of the ratchet plate.

If the scale square remains free from the support structure, the pawl 13does not relock into ratchet plate 12 at the release of the thumb lever17b, so that the thumb lever, in addition to its pivoting movement, mustalso be pressed inwardly which requires a force below the bolt 16. Atthis combined movernent the intermediate member 18 is pivoted and thepush rod is moved, which disengages the pawl 13. Besides, because of theinward pressure the operating member pivots in relation to theintermediate member 18 around the pivoting pin 16,

whereby the pin 22 is released by the intermediate member 18. Thepivoting is continued untilthe locking pin 23 locks behind the abutment20b. This position, in which the pawl 13 remains free until furtheroperation of the thumb lever, is shown in FIGS. 5 and 6. If the thumblever is raised somewhat, so that the locking pin 23 frees itself fromthe abutment 201:, the pawl 13 is brought back into engaged position bythe spring 24, whereby the shitting members 14, 15 and 18 return totheir original positions, shown in FIG. 1. The operating member isbrought again to the initial position by the spring 21, whereby the pin22 lies against the intermediate member What 1 Claim As My Invention AndDesire To Protect By Letters Patent Of The United States ls:

1. A device for locking a rotatable drawing head of a drafting machinehaving a rotatable support means with scale squares extending therefrom,a toothed ratchet plate secured to said support means, a lockpawlsrotatable into and out of engagement with the teeth of saidratchet, base means, said pawl being rotatably mounted on said basemeans, a hollow hand knob connected to said base means, a lock operatingthumb lever having a thumb engaging portion extending along the outsideof said knob and an arm portion'extending inside said knob, anintermediate link member rotatably pinned at one end to the arm portionof said thumb lever, said thumb lever being movable inwardly relative tosaid link member, a push rod pivoted at one end to the said one end ofsaid link member, said push rod acting against a transmission memberattached to said lock pawl, spring means normally urging said lock pawlinto ratchet contact, and lock pin means operable after a giveninward'movement of said thumb lever to move said link member with saidthumb lever and to thereby displace said push rod and transmissionmember and release said lock pawl from said ratchet plate upon continuedinward movement of said thumb lever, said lock pawl returning intocontact with the ratchet plate upon release of said thumb lever. Y

2. A device for locking a rotatable drawing head as defined in claim 1and further including means to retain said lock pawl out of ratchetplate engagement after release of said thumb lever.

3. A device for locking a rotatable drawing .head as defined in claim 1wherein said arm portion is of a length less than the thumb engagingportion and coil spring means urging said lock pin means against saidlink member after inward thumb lever movement commences.

4. A device for locking a rotatable drawing head as defined in claim 1,wherein said arm portion is bifurcated, said link member comprises twospaced similar plates within the bifurcated arm portion, and said pushrod being pinned between said plates.

5. A device for locking a rotatable drawing head as defined in claim 3,wherein the link member is pivoted at its other end to a bearing block,said bearing block being mounted on said base means.

6. A device for locking a rotatable drawing head as defined in claim5and further including a catch on said bearing block, said spring meansbeing connected at one end to said transmission member and at the otherto said catch,said bearing block also having a recess and said thumblever having a projection on the inside thereof, said coil springmeans'having one end engaging said projection and the other end thereofreceived in said recess.

7. A device for locking a rotatable drawing head as defined in claim 2wherein said means to retain said lock pawl out of ratchet plateengagement includes a bearing block mounted on said base means, saidbearing block having an abutment and a locking pin on the inside of saidthumb lever engageable against said abutment.

8. A device for locking a rotatable drawing head as defined in claim 1,wherein said hand knob is provided with a detachable cap.

1. A device for locking a rotatable drawing head of a drafting machinehaving a rotatable support means with scale squares extending therefrom,a toothed ratchet plate secured to said support means, a lock pawlrotatable into and out of engagement with the teeth of said ratchet,base means, said pawl being rotatably mounted on said base means, ahollow hand knob connected to said base means, a lock operating thumblever having a thumb engaging portion extending along the outside ofsaid knob and an arm portion extending inside said knob, an intermediatelink member rotatably pinned at one end to the arm portion of said thumblever, said thumb lever being movable inwardly relative to said linkmember, a push rod pivoted at one end to the said one end of said linkmember, said push rod acting against a transmission member attached tosaid lock pawl, spring means normally urging said lock pawl into ratchetcontact, and lock pin means operable after a given inward movement ofsaid thumb lever to move said link member with said thumb lever and tothereby displace said push rod and transmission member and release saidlock pawl from said ratchet plate upon continued inward movement of saidthumb lever, said lock pawl returning into contact with the ratchetplate upon release of said thumb lever.
 2. A device for locking arotatable drawing head as defined in claim 1 and further including meansto retain said lock pawl out of ratchet plate engagement after releaseof said thumb lever.
 3. A device for locking a rotaTable drawing head asdefined in claim 1 wherein said arm portion is of a length less than thethumb engaging portion and coil spring means urging said lock pin meansagainst said link member after inward thumb lever movement commences. 4.A device for locking a rotatable drawing head as defined in claim 1,wherein said arm portion is bifurcated, said link member comprises twospaced similar plates within the bifurcated arm portion, and said pushrod being pinned between said plates.
 5. A device for locking arotatable drawing head as defined in claim 3, wherein the link member ispivoted at its other end to a bearing block, said bearing block beingmounted on said base means.
 6. A device for locking a rotatable drawinghead as defined in claim 5 and further including a catch on said bearingblock, said spring means being connected at one end to said transmissionmember and at the other to said catch, said bearing block also having arecess and said thumb lever having a projection on the inside thereof,said coil spring means having one end engaging said projection and theother end thereof received in said recess.
 7. A device for locking arotatable drawing head as defined in claim 2 wherein said means toretain said lock pawl out of ratchet plate engagement includes a bearingblock mounted on said base means, said bearing block having an abutmentand a locking pin on the inside of said thumb lever engageable againstsaid abutment.
 8. A device for locking a rotatable drawing head asdefined in claim 1, wherein said hand knob is provided with a detachablecap.